Dielectric heating apparatus for tires

ABSTRACT

A method of and apparatus for heating moldable articles, such as pneumatic rubber tires, is disclosed utilizing an inner expandable bladder having an electrically conductive fluid, such as mercury, salt water, or woods metal. A source of high frequency energy in the range of, illustratively, from 1 to 60 megahertz is coupled between the conductive fluid and the metallic tire vulcanizing apparatus to rapidly heat the inner casing wall surfaces to the desired curing temperatures. A second outer bladder conforming to the casing walls contains a high dielectric constant low thermal loss fluid, such as silicone oil. The inner bladder is contoured to provide a greater volume of such fluid adjacent to the thinner sidewalls and thereby expose the heated conductive fluid closer to the thicker tire tread region. The heating field strengths are thereby distributed substantially uniformly in all parts of a moldable article having a nonsymmetrical cross-sectional configuration and it is maintained in the desired shape during heating.

United States Patent 1 Gilliatt DIELECTRIC HEATING APPARATUS FOR TIRES[75] Inventor: Charles L. Gilliatt, Andover, Mass.

[73] Assignee: Raytheon Company, Lexington,

Mass.

[22] Filed: Aug. 2, 1972 [2]] Appl, No.: 277,463

[52] US. Cl 219/1057, 219/1049, 219/1065, 425/41, 425/174.8

[51] Int. Cl. H05b 5/00, H05b 9/00, B29h 5/26 [58] Field 01' Search2l9/l0.81, 10.49, 219/1055, 10.57, 10.65; 425/41, 50,174.8

[56] References Cited UNITED STATES PATENTS 2,451,992 /1948 TeGrotenhui's 425/41 2,797,440 7/1957 Bauermeister 425/l74.8 X 2,782,4602/1957 Krug et a1. 425/174.8 X

Primary Examiner-C. L. Albritton Assistant Examiner-Hugh D. JaegerAttorney-Harold A. Murphy et al.

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HIGH FREQUENCY ENERGY SOURCE Nov. 6, 1973 [57] ABSTRACT A method of andapparatus for heating moldable articles, such as pneumatic rubber tires,is disclosed utilizing an inner expandable bladder having anelectrically conductive fluid, such as mercury, salt water, or woodsmetal. A source of high frequency energy in the range of,illustratively, from 1 to 60 megahertz is coupled between the conductivefluid and the metallic tire vulcanizing apparatus to rapidly heat theinner casing wall surfaces to the desired curing temperatures. A secondouter bladder conforming to the casing walls contains a high dielectricconstant low thermal loss fluid, such as silicone oil. The inner bladderis contoured to provide a greater volume of such fluid adjacent to thethinner sidewalls and thereby expose the heated conductive fluid closerto the thicker tire tread region. The heating field strengths arethereby distributed substantially uniformly in all parts of a moldablearticle having a nonsymmetrical cross-sectional configuration and it ismaintained in the desired shape during heating.

10 Claims, 2 Drawing Figures CONDUCTIVE FLUID HIGH DIELECTRIC LOW LOSSFLUID HEAT SOURCE CONTROLS PAIENIEDnuv sum 3.770.931

SHEET 10F 2 HIGH FREQUENCY ENERGY SOURCE PAIENIEDunv ems 3770.931

SHEET 2 0F 2 62 CONDUCTIVE FLUID HIGH DIELECTRIC LOW LOSS FLUID TANK TOTANK FREg L E NcY HEAT ENERGY SOURCE CONTROLS DIELECTRIC HEATINGAPPARATUS FOR TIRES BACKGROUND OF THE INVENTION 1. Field of theInvention The invention relates to the heating of moldable articles byhigh frequency electromagnetic energy.

2. Description of the Prior Art Dielectric heating utilizing highfrequency altemating fields has found wide acceptance in the treatmentof inherently poor thermal conductors, such as paper, wood, leather andrubber articles. For the purposes of the present application the termhigh frequency is defined as electromagnetic energy in that portion ofthe spectrum having frequencies of under 60 megahertz. Numerous sourcesare known in the art including vacuum tubes and the energy is typicallycoupled to the article by conductive electrodes. In the utilization ofsuch energy typically a nonsymmetrical and nonhomogenous mass ispresented to the oscillating fields. The distribution of theelectromagnetic energy within the product, therefore, becomes a functionof the varied dielectric constants of the load as well as the powerfactor. This latter characteristic represents the amount of currentwhich will flow through the mass and produce a heat loss. In thedielectric heating art the dielectric constant value and power factorare multiplied to obtain a measure of total loss. It is evident,therefore, that the physical properties of the materials as well asdistribution of the oscillating fields is of primary consideration indielectric heating applications.

One product which is an inherent poor thermal conductor is the pneumatictire which is typically cured at elevated temperatures by steam or othermeans at temperatures of above 300 F. During the curing cycle the moldis heated and steam under pressure is generally applied within the tirecasing walls by such means as a bladder of rubber or the like. The tirevulcanization process is time consuming and involves expensive andcumbersome apparatus. Such moldable article has a nonsymmetricalcross-sectional configuration with thin sidewalls and a thick tire treadregion defining a sub stantially hollow interior. The variation incrosssectional dimensions leads to problems with uniform heatdistribution during the curing cycle. The search, therefore, for new andimproved methods and apparatus for the heat treatment of moldablearticles continues in industry.

SUMMARY OF THE INVENTION In accordance with the present invention amethod and apparatus for dielectrically heating moldable articles isprovided with uniform distribution of the high frequency electromagneticenergy in all parts involving the use of expandable bladder members withtwo types of fluids. An inner expandable member contains an electricallyconductive fluid and an electrode from the high frequency energy sourceis connected directly to the fluid. Surrounding the inner bladder memberis a second outer expandable bladder member containing a high dielectricconstant low loss fluid. The inner member is contoured to provide agreater volume of low loss fluid and thereby space the conductive fluidfurther away from the thinner sidewalls, for example, a pneumatic tire.The greater concentration of heat is, therefore, directed toward thethicker tire tread portions where the wall thickness is substantial. Thefluids may also be heated to assist in curing times. The distribution ofheating energy fields is maintained uniform throughout the curing cycle.

The invention is readily adaptable to existing tire vulcanizing moldapparatus using steam heat to raise the temperature of the moldcavity-defining members and platens. After curing the fluids are drainedfrom the bladder members to reservoir means and the upper cavity memberis pivoted away by hydraulic means to permit removal of the tire forcooling and post cure inflation. While rubber articles are describedherein the invention is equally applicable to any moldable article of aninherently poor thermally conductive material including articles of anynumber of thermoplastic material.

BRIEF DESCRIPTION OF THE DRAWINGS Details of the invention will bereadily understood after consideration of the following description ofthe preferred embodiment and reference to the accompanying drawings,wherein:

FIG. 1 is an isometric view of the embodiment of the invention; and

FIG. 2 is a partial cross-sectional view of the embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT The apparatus 10 embodying theinvention comprises upper and lower mold annular cavity-defining members12 and 14 supported by legs 22. A lid I6 controlled by a hydraulicmechanism 18 is provided with a connecting bracket 20 for pivotalmovement thereof after the curing cycle has been completed. A shaft 24disposed within a concentric tubular holder 26 is internally connectedto the means for movement of the bladder members, to be hereinafterdescribed, to provide for removal and insertion of such bladder membersin the interior of the tire casing at the commencement and terminationof the curing cycle. The shaft moves upwardly and is controlled by meansof a gear box 28 having an eccentric sheave 30 coupled to a rod 32 witha lever arm assembly 34 pivotally secured to bracket 36 on the undersideof the lower cavity member 14. A motor is also provided and is notillustrated for the sake of clarity.

Referring now to FIG. 2, upper and lower mold cavity-defining members 12and 14 comprise top and bot- I tom half sections 38 and 40 adapted tomate and define the shaping and tread vulcanizing walls within which anannular moldable article, such as an uncured tire 50 having asubstantially hollow interior, is disposed. A lip portion 42 and 44provides mating surfaces for the joined mold members 12 and 14 duringthe curing cycle. Each of the half sections 38 and 40 have abutting topand bottom steam-heated platen members 46 and 48 secured thereto.Typically, in such apparatus, steam is continuously introduced into theplatens to elevate the mold temperatures to approximately 310 to 350 Fwhich is the normal curing temperature for passenger tires.

Within the casing of the uncured or green tire 50 bladder members 52 and62 are disposed. Bladder member 52 which is referred to herein as theouter bladder member conforms to the tire casing walls. The ends ofouter bladder 52 are provided with enlarged feet 54 and 56 to form anannular bead disposed within anchoring channels in lower fixed clampingring 58 and upper movable clamping ring 60. This arrangement provides afluid-tight structure when a fluid is pumped within the bladder 52during operation. A similar arrangement provides enlarged feet 64 and 66for securing the inner bladder member 62 to the clamping rings 58 and60. A piston rod member 68 is joined to the vertically displaced shaft24 and is secured by a clamp 70 to the upper clamping ring 60. The rodextends within a hub 72 having cylindrical cap 74 joined by bolts 76 tothe lower clamping ring member 58. Upward movement of the rod 68 resultsin the drained bladders assuming a shape which will permit ready removaland insertion of the tire casing.

Clamping ring member 58 defines inner passageways 78 at a number ofpoints around the annulus of the tirecasing to permit the introductionof a fluid 79 within the outer bladder member 52. Line 80 threadablyengages the passageways and is connected by a check valve 82 andregulator valve 84 to a reservoir tank 86 containing fluid l. The fluidsin the practice of the invention are desirably heated by any suitablesource designated by the numeral 88 and all the electrical controls forthe operation of the apparatus are designated by the box 90. Fluid 1 isof a high dielectric constant low thermal loss characteristic, such assilicone oil, and is utilized for spacing of the heat source, to behereinafter described, with relation to the nonuniform walls of the tirebeing cured.

As electrically conductive fluid 92 is introduced within the innerbladder member 62 by passageways 94 which are electrically insulatedfrom the clamping ring 58 by a nonconductive line 96 forming a conduitfor the introduction of the fluid ll. Line 96 incorporating a checkvalve 98 and regulator valve 160 is coupled to tank 102 which is alsoconnected to the controls 90. An illustrative fluid having the desiredelectrically conductive characteristics comprises mercury, salt water orwoods metal. The latter material woods metal describes a low temperaturealloy containing bismuth, antimony and tin of the type often employed inautomatic sprinkler heads.

A suitable high frequency electromagnetic energy source 104 having anoperating frequency of around 40 megahertz is controlled by a relay 16having contacts 108 coupled to electrical controls 90. Coaxial electrode110 is connected to a metallic sleeve 112 surrounding the insulated line96 which is connected to the ring 114 of the grounded tire moldingapparatus. Center electrode 116 has inner end 113 disposed directly inthe conductive fluid 92 to complete the circuit for the raising of thetemperature of the conductive fluid to the temperature required to heatthe inner casing walls. A diaphragm 120 is coaxially disposed asindicated to prevent backup of the electrically conductive fluid 92 tothe high frequency source.

At the beginning of the curing cycle with the upper mold member 12raised the uncured tire casing is placed in the cavity around thebladders members 52 and 62. Upon the closing of the apparatus andfilling bladder 52 containing the low loss material having a highdielectric constant assumes the shape conforming to the inner casingwalls. The inner bladder 62, however, is contoured so as to be closer tobladder 52 at the point adjacent to the thick tread of the tire casing50. 6

A greater volume of the heating conductive fluid 92 is therebyconcentrated adjacent to the thicker tread region. The thinner sidewallportions are protected from excessive heating by the interveningfluid-79 to provide a more uniform heat distribution arrangementresponsive to a nonsymmetrical article. After the curing, the lines withboth fluids are drained and the upper mold member 12 is again raised andpivoted to permit removal of the treated product for cooling andpostcure inflation.

Since numerous modifications in the preferred embodiment disclosedherein as well as alternative materials, such as those of thethermoplastic composition will become apparent to those skilled in theart, a broad interpretation of the invention as defined in the appendedclaims is intended.

I claim:

1. In combination:

apparatus adapted to support and mold an article having a substantiallyhollow interior;

expandable bladder members including an outer member conforming to thecontour of said interior wall surfaces and an inner member disposedwithin said outer member;

means for filling said outer member with a fluid having a highdielectric constant low thermal loss characteristic and means forfilling said inner member with an electrically conductive fluid; and

means for dielectrically heating said article including a source of highfrequency electromagnetic energy coupled to said electrically conductivefluid.

2. The combination according to claim 1 wherein the wall surfacecontouring of said inner bladder member is such that the electricallyconductive fluid is closer to selected regions of said article thanother regions.

3. The combination according to claim 1 wherein said apparatus andfluids are heated.

4. The combination according to claim 1 wherein said moldable articlecomprises an annular nonsymmetrical cross-sectional configuration andthe wall surface contouring of said inner bladder member is such thatsaid electrically conductive fluid is closer to the thickercross-sectional region than the thinner regions.

5. The combination according to claim 1 wherein said moldable articlecomprises a pneumatic tire.

6. The combination according to claim 1 wherein said conductive fluid isselected from the group including mercury, salt water and a lowtemperature alloy composed of bismuth, antimony and tin.

7. The combination according to claim 1 wherein said high frequencyenergy source has a range of from 1 to 60 megahertz.

8. Apparatus for dielectrically heating moldable articles comprising:

an enclosure defining an annular cavity adapted to receive and shape anarticle having a substantially hollow interior;

means for heating said enclosure walls to a desired elevatedtemperature;

expandable means including outer and inner bladder members disposedwithin said interior wall surfaces and means for filling said outermember with a fluid having a high dielectric constant low thermal losscharacteristic and said inner member with an electrically conductivefluid to maintain pressure against and heat said article within saidcavity during operation;

said inner member wall surfaces being contoured to provide for a closerspacing of said conductive fluid to selected regions of said article;and

3,770,931 6 a high frequency electromagnetic-energy source cou- 10. Theapparatus according to claim 8 wherein said pled to said electricallyconductive fluid. conductive fluid is selected from the group including9. The apparatus according to claim 8 and means for mercury, salt waterand a low temperature alloy comraising a portion of said enclosure topermit insertion posed of bismuth, antimony and tin. and removal of saidarticle. 5

1. In combination: apparatus adapted to support and mold an articlehaving a substantially hollow interior; expandable bladder membersincluding an outer member conforming to the contour of said interiorwall surfaces and an inner member disposed within said outer member;means for filling said outer member with a fluid having a highdielectric constant low thermal loss characteristic and means forfilling said inner member with an electrically conductive fluid; andmeans for dielectrically heating said article including a source of highfrequency electromagnetic energy coupled to said electrically conductivefluid.
 2. The combination according to claim 1 wherein the wall surfacecontouring of said inner bladder member is such that the electricallyconductive fluid is closer to selected regions of said article thanother regions.
 3. The combination according to claim 1 wherein saidapparatus and fluids are heated.
 4. The combination according to claim 1wherein said moldable article comprises an annular nonsymmetricalcross-sectional configuration and the wall surface contouring of saidinner bladder member is such that said electrically conductive fluid iscloser to the thicker cross-sectional region than the thinner regions.5. The combination according to claim 1 wherein said moldable articlecomprises a pneumatic tire.
 6. The combination according to claim 1wherein said conductive fluid is selected from the group includingmercury, salt water and a low temperature alloy composed of bismuth,antimony and tin.
 7. The combination according to claim 1 wherein saidhigh frequency energy source has a range of from 1 to 60 megahertz. 8.Apparatus for dielectrically heating moldable articles comprising: anenclosure defining an annular cavity adapted to receive and shape anarticle having a substantially hollow interior; means for heating saidenclosure walls to a desired elevated temperature; expandable meansincluding outer and inner bladder members disposed within said interiorwall surfaces and means for filling said outer member with a fluidhaving a high dielectric constant low thermal loss characteristic andsaid inner member with an electrically conductive fluid to maintainpressure against and heat said article within said cavity duringoperation; said inner member wall surfaces being contoured to providefor a closer spacing of said conductive fluid to selected regions ofsaid article; and a high frequency electromagnetic-energy source coupledto said electrically conductive fluid.
 9. The apparatus according toclaim 8 and means for raising a portion of said enclosure to permitinsertion and removal of said article.
 10. The apparatus according toclaim 8 wherein said conductive fluid is selected from the groupincluding mercury, salt water and a low temperature alloy composed ofbismuth, antimony and tin.